Plasma characterization and process control diagnostics

Abstract

Diagnostics are needed both for plasma characterization and for plasma processing control. Normally, different diagnostics are employed. Process control relies on the ability to measure data dependent on charged and neutral particle parameters as well as on in situ surface diagnostics. Gas phase diagnostics employed at the University of Wisconsin Engineering Research Center for Plasma-Aided Manufacturing provide examples of both types of diagnostics. Both invasive and noninvasive diagnostics are employed. Invasive diagnostics such as probes are useful for characterizing the plasma but are usually not useful for control. Control is best provided by noninvasive diagnostics. Many noninvasive diagnostics, such as laser induced fluorescence are not suitable for control because they are too finicky or too inconvenient to use. Because monitoring the process in situ usually doesn’t work, it is recommended that characterization be aimed at identifying key parameters to be used for control. The specific problem of controlling the SiO2 etch rate with CF4/O2/CHF3/Ar in an electron cyclotron resonance tool is discussed as an example of this approach. The current status of our attempts at real-time control is given.